1. Field of the Invention
The present invention relates to an impact absorption structure of vehicle seat which is so designed that a local part of seat frame is deformable to absorb an impact caused by a great load applied to the seat in the case of a rear-end collision, or in the case of a backward collision wherein, when a vehicle runs backwardly, a backward side of vehicle collides with something hard or other vehicle.
2. Description of Prior Art
When a rear-end collision or a backward collision defined above occurs to a vehicle, a great load is applied from a seat occupant to a seat in the vehicle in a backward direction, thus creating a corresponding great impact to a whole of the seat. That is, a great impact thus created is transmitted from a seat back of the seat through an upper body portion of an occupant sitting on the seat and imparted to the seat.
Normally, the vehicle seat itself is formed by robust seat frames sufficient to withstand such impact load, for which reason, the load or impact is transmitted straight through the seat frames and intensively exerted upon a relatively vulnerable portion of mechanical part provided in the seat frames, such as seat adjustment devices including a linkage of seat height adjustment mechanism. In that case, it is highly possible that the mechanical parts or linkage of such seat height adjustment device or a connection portion between the seat cushion frame and a floor will be damaged or broken.
In order to solve the forgoing problem, a deformable area is defined in a particular point in the seat frame to effectively absorb the impact and prevent an extensive exertion of the impact on foregoing linkage or the connection portion of seat adjustment mechanism provided between the seat cushion frame and floor.
One example of such shock absorption arrangement is found from the Japanese Laid-Open Patent Publication No. 7-132767, which teaches a vehicle seat structure wherein a side frame member of the seat back thereof is provided with a deformable area at a predetermined point therein, so that the deformable area will be deformed by an impact load applied to the seat back, to thereby absorb most of the impact load.
However, in this shock absorption structure of seat-back side frame members, it is difficult to adjust and define the deformable area in an optimum size for each different seat back, and further, there is no disclosure for provision of means for limiting backward inclination of the seat back in the case of the deformable area being deformed to allow such backward inclination. Hence, it is more likely than not that the seat back will be subjected to excessive backward inclination in a collision case.
On the other hand, as disclosed by the Japanese Laid-Open Patent Publication No. 2002-12072, the foregoing locally deformable arrangement is provided in a side frame member of seat cushion frame to effectively absorb the impact load. According to this prior art, the side frame member is connected with a seat slide device and a sector-like deformable area is defined in an accordion fashion in the upper flange portion of the side frame member. With this arrangement, in a backward collision case, the connection point between the side frame member and the seat slide device serves to limit excessive deformation of the seat cushion side frame section as well as excessive backward inclination of the seat back, and also, the sector-like deformable area is deformed to absorb the impact load.
Incidentally, there is known a low-type seat cushion frame which is reduced in height to lower a position of buttock portion of an occupant on the seat cushion frame. This type of seat is, in most cases, a so-called slide seat which is provided with a slide device at the bottom side thereof to permit its fore-and-aft movement. In this particular sort of seat, each side frame member of the seat cushion frame is naturally reduced in its height-wise thickness and therefore decreases its rigidity. For that reason, typically, the side frame member per se is formed by four walls so as to have a closed cross-section to increase its rigidity.
With regard to the Japanese Pub. No. 2002-12072, the side frame member thereof is basically formed by four walls to have the above-described closed cross-section structure, but an upper wall is partly opened in the four walls of the side frame member due to the sector-like deformable area being formed in an accordion fashion in the upper flange portion. Such shock absorption structure is defective in that the thus-processed flange portion of the side frame member does not serve its reinforcing and protection functions. That is, the deformable region given in the upper flange portion of side frame member is found defective in decreasing its reinforcement for the upper side of the side frame member itself and does not protect the adjacent trim cover and padding of seat cushion.